Many tractors are equipped with fifth wheel assemblies which may be locked in different positions with respect to the tractor to distribute the load from the trailer at different points along the tractor frame. Load distribution is important not only for the handling of the tractor trailer rig, but is also important for axle loading limits which vary between different states. The usual method of repositioning the fifth wheel was for the driver to unlock the locking mechanism of the fifth wheel, lock the wheels of the trailer and drive the tractor forward and back thereby moving the fifth wheel with respect to the tractor frame followed by locking the fifth wheel in a new position. This required the driver to leave the tractor to unlock the fifth wheel and also to lock the fifth wheel in its new position. It also required the trailer wheels to be locked during this moving operation. Furthermore, the exact amount of movement of the fifth wheel was depended upon the distance that the tractor was moved and was therefore inherently inexact.
Various other attempts have been made to provide adjustable fifth wheel assemblies but these devices have required elaborate and expensive replacement of the existing fifth wheel mounting assembly and generally have not permitted the movement of the fifth wheel without the locking of the trailer wheels. Various fifth wheel mounting and moving devices are shown in the following U.S. Pat. Nos.: 2,807,477; 3,170,716; 3,181,889 and 3,391,948.
The devices shown in the above-listed patents have not permitted the economical modification of existing fifth wheels, and there is a need for a relatively inexpensive, easily operated device for attachment to existing fifth wheel asemblies to facilitate the movement of the fifth wheel assembly with the respect to the tractor frame.